Plasmon-enhanced high order harmonic generation of open-ended finite-sized carbon nanotubes: The effects of incident field's intensity and frequency and the interference between the incident and scattered fields

The nonlinear optical properties of hybrid systems composed of a silver nanosphere and an open-ended finite-sized armchair single-walled carbon nanotube (SWCNT) are systematically investigated by the hybrid time-dependent Hartree-Fock (TDHF)/finite difference time domain (FDTD) approach, which combines the real-time TDHF approach for the molecular electronic dynamics with the classical computational electrodynamics approach, the FDTD, for solving Maxwell's equations. The high order harmonic generation (HHG) spectra of SWCNTs are studied as a function of the intensity (I₀) and frequency (ω₀) of the incident field, and SWCNTs length as well. It is found that the near field generated by a Ag nanoparticle has an overall enhancement to the molecular HHG in all the energy range, and it extends the HHG spectra to high energy. The inhomogeneity of the near field results in the appearance of even-order harmonics, and their corresponding spectral intensities are sensitive to ω₀, therefore the near field's gradient. When ω₀ is far away from the frequency of plasmon resonance of the silver nanosphere (ω_c), the interference between the incident and scattering light beams extends the spectral range and makes the HHG spectra more sensitive to I₀, while at ω₀ = ω_c, the impact of the interference on the spectra is negligible.